Digital frontends or color print servers geared to prepare data and drive digital printers can be described in general terms by two major parts as is depicted in FIG. 1:                1. A frontend element 11 processes digital files in a form of a page description language (PDL) 13, such as, for example, PostScript (PS). The frontend element 11 is equipped with PDL processing means, and the output of the processing means is data 14 in a ready-to-print (RTP) form.        2. A backend element 12 receives the RTP data and sends it to a digital printer for printing via a video interface 15 to the printer.        
Most of color print servers produce the RTP data buffers in line with the print engine, in other words, the data that is generated by the frontend 11 is immediately consumed by the backend 12, without a step of generating RTP objects and saving them on an intermediate storage for further printing. One line of commercial color print services uses the above method of intermediate RTP generation, and defines a special RTP format and a data flow based on the RTP format. The RTP format consists of reusable as well as from non-reusable elements which are represented as separate RTP elements.
Frontend 11 receives incoming PDL jobs in, for example, a page definition file (PDF), PS or variable PostScript (VPS). Frontend 11 processes the jobs, and converts the PDL to RTP jobs. Backend 12 merges and assembles the RTP elements into page-bitmaps and outputs the bitmaps to the printer using a video interface 15.
The use of intermediate saved RTP format is to better for meeting the digital printer's engine speed. For non-variable data printing (VDP) jobs, multiple copies are printed at the engine speed. This is achieved by preparing the RTP once and printing the RTP multiple times. In the case of typical VDP jobs, the RTP is prepared at engine speed.
The strict division between the frontend and the backend elements when designing an interface to new printer is a very important. The frontend is a printer-independent part and typically requires limited customization, while the backend is a printer-dependent part and typically requires specific customization to accommodate specific printer needs. FIG. 2 is a top-level view of a typical commercial color print server illustrating the separation between the frontend 11 and the backend 12 as discussed above.
An important element in the printer color server architecture is the merger and printer interface boards 28. A merger-board merges and assembles RTP elements in real-time at the engine speed. The rest of the system can be viewed as a production line and its main purpose is to produce a plurality of RTP object in order to feed the merger-boards. This view of the system is convenient, however, other alternative views are possible as well.
RTP format is a proprietary format of the Eastman Kodak Company for ripped jobs. According to this format, a ripped job consists of RTP pages and each page refers to RTP elements. RTP is an element-based format and rendered reusable and non-reusable elements are represented as separate RTP elements. Each RTP element can be viewed as a compressed raster-element. RTP is prepared accordingly to accommodate the specifics of the fusion cards and engine characteristics.
Processing frontend 11 consists of the following main components:                Job input 22, responsible for importing jobs to the system;        Raster image processor (RIP) 23;        Image processing components 24 for transformations of raster data produced by RIP 23;        RTP preparation module 25.        
As described above, the frontend 11 receives incoming PDL jobs 13 and converts them to RTP format 14. PDL-to-RTP is a multi-step operation that consists of the following processing steps:                1. The job is received and imported to the system.        2. The job is scheduled for processing.        3. The pipelined job processing starts by RIP 23, image processing 24 such as trapping and anti-aliasing.        4. RTP preparation module 25 transforms the final raster-data to RTP format 14.        5. RTP format 14 is further stored to RTP storage 26.        
All the above steps are performed in pipelined fashion. For example, trapping may start after a few raster scanlines are RIPed and RTP creation may start after a few raster scanlines on the page are prepared.
Printing backend 12 consists of the following components:                1 RTP storage 26—an efficient raster-element storage that guarantees reading of raster-elements at print engine speed. RTP storage is typically implemented as a fast disk or a disk-array. This enables a large storage capacity at high-speeds as dictated by the engine speed.        2. Data feeder 27—a component that schedules work for merger card/cards. It is responsible for loading RTP layout, initiating merge operations, and monitoring merge process.        3. Merger boards 28—the components responsible for merging and assembling RTP elements into final page-bitmaps and sending said bitmaps to the print engine.        
As described above the backend 12 is responsible for printing RTP data at the engine speed. This includes the following operations:                1. Reading RTP-data from RTP-storage.        2. Merging and assembling RTP-data into contone page-bitmaps.        3. Additional processing (screening, compression, and look-up table transformation (LUT)) might be applied to contone bitmaps according to engine specification.        4. Outputting bitmaps via the printer video interface 15 to the print engine.        5. Controlling the engine.        
The main operations performed by the backend are the operations of merging and assembling of RTP data to the resulting bitmaps. Though the merging process can be implemented either in software or in hardware, typically the merger is implemented in hardware in order to meet printer engine speed.
According to the performance requirements, there could be a single merger board or multiple merger boards in the system. In a printer color server equipped with a single merger board 28, the board will handle all the process colors (e.g. Cyan (C), Magenta (M), Yellow (Y) and Black (K)). In a printer color server equipped with multiple merger boards each board can be responsible for one or more process colors. For example, in the case of two merger boards 28, one board will handle C and M color channels 53 whereas the other board will handle Y and K colors.
The requirements of color digital printers are getting more and more demanding. Printers capable of printing one hundred A4 color pages per minute (100 ppm) are already available. Printers that will print more than 1000 ppm will be introduced in the near future. The current architecture of color servers is not capable to drive the high speed printers at the required speed and there is a need to reengineer the process to meet the new requirements.